The proposed work for this research project includes the investigation of the fundamental mechanisms involved in the regulation of ventilation at rest and during exercise in physiological and pathological states. The analytic approach of the functional components of the respiratory system is extended to a synthetic analysis of the totality of this system with considerations of the integrative actions of the multiple stimuli that control ventilation with the aid of an analog computer. Experiments were concerned with the breath-by-breath analysis of the V-Pco2 response at rest, during exercise with CO2 inhalation and/or induction of hypoxia. These experiments were carried out in normal subjects and in patients with lung disease.